Microwave spectrometers have been used to measure the concentration of a specified gas in gas samples or sample atmospheres. For instance, microwave spectrometers have been employed in ethylene oxide sterilization systems to measure the concentration of ethylene oxide gas in gas samples obtained from ethylene oxide sterilization chambers. One such microwave spectrometer is disclosed in the publication entitled Specificity, Accuracy, And Interpretation Of Measurements Of Ethylene Oxide Gas Concentrations During Sterilization Using A Microwave Spectrometer published in the Rev. Sci. Instrum. (68) 7, Jul. 1997, which is incorporated herein by reference. The measurement obtained from the microwave spectrometer can be used to determine if a sufficient quantity or concentration of ethylene oxide gas which is necessary to sterilize the articles in the sterilization chamber is present in the sterilization chamber. If a sufficient concentration of ethylene oxide gas is present in the sterilization chamber for a predetermined minimum period of time and certain other conditions are satisfied, the articles being sterilized may be released to the marketplace as properly sterilized. This release of the articles based on the level of ethylene oxide in the sterilization chamber and other conditions without reliance on biological indicators is generally referred to as parametric release.
The relative humidity of the atmosphere in a sterilization chamber during the sterilization process is one of the conditions which may affect the effectiveness of the ethylene oxide sterilization process. For example, in certain ethylene oxide sterilization chambers, if the relative humidity in the sterilization chamber is above a certain percentage (i.e., approximately thirty-three percent) or below a certain percentage (i.e., approximately ninety percent), the interaction between the ethylene oxide gas and the articles being sterilized in the chamber may vary and may affect the sterilization process. Accordingly, to accomplish parametric release for the ethylene oxide sterilization process, it is necessary to know the relative humidity of the atmosphere inside the sterilization chamber during the sterilization process.
Various apparatus are known to measure the relative humidity in a gas sample or sample atmosphere. Furthermore, microwave spectrometers have been tested for measuring concentration of both ethylene oxide and water vapor. One such microwave spectrometer is disclosed in the publication entitled A Microwave Spectrometer With A Frequency Control System Employing A Frequency “Scanning Window” Locked To The Rotational Absorption Peak published in the Rev. Sci. Instrum. 66 (10), October 1995, which is incorporated herein by reference. This system employed a single microwave detector and used a dew point generator for calibration of the instrument for measuring water vapor. However, the dew point generator did not function adequately. A need therefore remains for an accurately calibrated microwave spectrometer which accurately and reliably measures the concentration of ethylene oxide and the concentration of water vapor in one or more gas samples taken from an ethylene oxide sterilization chamber and determines the relative humidity in the gas samples.